Field of the Invention
This invention relates to a printing process and apparatus for testing deposition of liquid compositions on a surface. In particular, depositing liquid compositions on a proofing device containing a gradient of ink containment structures arranged in columns and having gaps between adjacent ink containment structures. The gaps can be constant or increase in magnitude when progressing through the column of ink containment structures. The gradient in gaps, print areas, and shape of the top surface allows evaluation of printing ink liquid compositions, as well as properties of the top surfaces. This proofing device promotes rapid evaluation of wetting characteristics on the top surface of the ink containment structures.
Description of the Related Art
An electronic device can include a liquid crystal display (“LCD”), an organic light-emitting diode (OLED) display, or the like. The manufacture of electronic devices may be performed using solution deposition techniques, or alternatively, vapor phase techniques. For solution deposition, one process of making electronic devices is to deposit organic layers over a substrate, also referred to as a backplane when containing electronic elements, by printing (e.g., ink-jet printing, continuous printing, etc.). In a printing process, the liquid composition, also called ink, being printed includes an organic material in a solution, dispersion, emulsion, or suspension with an organic solvent, with an aqueous solvent, or with a combination of solvents. After printing, the solvent(s) is(are) evaporated and the organic material remains to form an organic layer for the electronic device.
The OLED devices produced by such processes utilize one or more layers of organic semiconductor materials laminated with other supporting layers, and sandwiched by two electrodes, these devices are used in many different kinds of electronic equipment.
Several methods for providing ink containment for OLED devices are described in the literature. These are based on containment structures, surface tension discontinuities, and combinations of both. The testing of new inks, or new formulations upon which the ink is deposited, is an expensive procedure when using operational backplanes containing requisite electronic elements. In addition, variables such as pixel area, pixel shape, and linear separation between pixels is not accommodated when employing existing backplanes.
In addition, surface tension discontinuities are obtained when there are either printed or vapor deposited regions of low surface tension materials. These low surface tension materials generally must be applied before printing or coating the first organic active layer in the pixel area. Generally the use of these treatments impacts the quality when coating continuous non-emissive layers, so all the layers must be printed.
Each organic semiconductor material can be carried in a liquid composition. During manufacture of a device each liquid composition is dispensed from a dedicated nozzle assembly. The nozzle assemblies are grouped in nozzle sets, with one nozzle in each set dispensing a particular color of ink. Each nozzle assembly dispenses liquid and deposits that liquid along a longitudinal lane that extends across a backplane of the device. The nozzle assemblies in each nozzle set dispense a liquid composition into a respective lane. The nozzle assemblies can be located within a printhead, and the printhead travels in a linear path in a first or forward direction, in addition to a second or reverse direction, while printing the liquid composition on the backplane.
Liquid printing can be conducted in either non-continuous or continuous operation as disclosed in the prior art. The deposition of the liquid composition in a continuous operation leads to a portion of the liquid composition being deposited outside the bounds of the substrate, or between active pixel areas of the electronic device, and this portion is either recycled or lost. Closer spacing between adjacent pixels leads to higher resolution of resulting displays, as referenced by the PPI (pixels-per-inch) designation of modern display units. This requirement for ever higher PPI designs requires tighter control for liquid deposition. In particular, the ink must “break” cleanly during deposition to fully cover the desired print area without forming a bridge to the neighboring print areas.
Non-continuous, or discrete liquid deposition, include various methods used in digital printing including: ink-jet; continuous ink-jet (CU); drop-on-demand (DOD), using thermal or piezoelectric DOD. Continuous liquid deposition can include nozzle or slot die coaters among several choices where a continuous stream of ink is emitted, but only discrete areas are intended to capture the ink.
In other words, any adjustment to the ink formulation, or to compositions defining the top layer of the print areas, requires testing and optimization of the printing process. This optimization can be time consuming and expensive to conduct. Accordingly, any printing process changes made for production level manufacturing can result in pixels containing too little or too much ink. This is a continuing problem, and the testing solutions have not met the required level of time and cost levels required for printing of organic electronic devices. In view of the foregoing it is believed additional improvement is required to optimize print processing for organic electronic devices.